Acidic partial esters as lubricating oil additives



United States Patent 3,029,204 ACIDIC PARTIAL ESTERS AS LUBRICATING OILADDITIVES Alfred H. Matuszak, Westfield, and Stephen J. Metro, ScotchPlains, N.J., and John Samuel Paul Schwarz, Dugway Proving Ground, Utah,assignors to Esso Research and Engineering Company, a corporation ofDelaware No Drawing. Filed May 12, 1959, Ser. No. 812,583

9 Claims. (Cl. 252-56) This invention relates to lubricating oiladditives for improving the load-carrying ability of a lubricant and forinhibiting corrosion of lead. Particularly, the invention relates tosynthetic ester lubricating oil compositions containing acidic partialesters which are prepared by esterification reactions betweendicarboxylic acids and glycols.

The use of various fully esterified aliphatic diesters and complexesters as synthetic lubricating oils is well known to the art and hasbeen described in numerous patents, e.g. US. 2,723,286; 2,743,234; and2,575,196. In general, these prior aliphatic synthetic ester lubricatingoils are characterized by viscosity properties that are outstanding atboth low and high temperatures, especially when compared to minerallubricating oil. Because of these characteristics, the synthetic esteroils have become of increasing importance in the field of lubrication.And one of the most important current applications of such compounds isin the lubrication of aviation gas-turbine systems such as are used inthe turbo-jet or turboprop type of aircraft. However, in general, theloadcarrying ability of the aliphatic ester oils is not particularlyhigh. Because of the increasing severity of the conditions prevailing inthe lubrication of aviation gas-turbine systems it is highly desirableto form synthetic ester lubricating compositions which have higherload-carrying ability than is now generally available. At the same timethe composition should be noncorrosive to lead in the copperleadbearings generally present in aircraft engines. It has now been foundthat the acidic partial esters of this invention are very effective insynthetic ester lubricating oil compositions not only for improvingload-carrying ability but also for inhibiting lead corrosion by theester oil. At the same time, these new additive materials do not undulyattack copper, magnesium, aluminum or silver which are generally alsopresent in the engine.

The acidic partial esters of the invention are believed to berepresented by the following formula:

Dibasic AcidGlycol-(Dibasic Acid-Glycol),,-Dibasic Acid wherein x is anumber of 0 to 4. This acidic material is prepared by simpleesterification reactions between a glycol and a dicarboxylic acid usingabout 1.2 to 2.0, preferably 1.7 to 2.0 moles of the dicarboxylic acidper mole of the glycol. When using two moles of acid per mole of glycol,the primary product is believed to have the formula: DibasicAcid-Glycol-Dibasic Acid, i.e. x is 0. However, minor amounts of longerchain mole cules are undoubtedly also present, i.e. where x is l ormore, and the exact composition is not known with certainty.

The dicarboxylic acids used in preparing the acidic partial ester willinclude the C to C alkandioic acids, such as adipic, sebacic, azelaicand isosebacic acid. The isosebacic acid is a mixture of C acidscomprising about 60 to 90 weight percent of wethyl suberic acid, aboutto 25 weight percent of m,a-diethyl adipic acid, and about 5 to 15weight percent of sebacic acid. A typical acid will contain about 75weight percent of a-ethyl suberic acid, about 15 weight percentofa,a'-diethyl adipic acid and about weight percent of sebacic acid.

The glycol, which is used, may be either an alkylene ice glycol or apolyalkylene glycol, said glycol containing a total of 2 to 36,preferably 4 to 18, carbon atoms. Thus, included in the invention areethylene glycol, propylene glycol, butanediol-1,4, pentanediol-1,5;hexanediol-l,6, octylene glycol, and other straight or branched chainhydrocarbon glycols. Operable polyglycols will include polyethyleneglycols of the formula HO (CH CH O CH CH OH wherein n is 1 to 17,preferably 1 to 8, and polypropylene glycol of the formula l '1: 1 l aHO(CHCHO)nCH-CHOH wherein either R or R is a methyl group and the otheris hydrogen, and n is l to 11, preferably 2 to 5.

The esterification reaction is preferably carried out in the absence ofan esterification catalyst. While the reaction will take place morerapidly with a catalyst, a catalyst is not used in order to obtain. apurer reaction product and to avoid washing procedures to eliminate thecatalyst. If desired a water entraining agent such as heptane or toluenemay be used.

The ester oils operable as base oils in the compositions of thisinvention comprise hydrocarbon chains interrupted with ester linkages.The hydrocarbon chains may be further interrupted with ether ortlrioether linkages. Such esters will include diesters, polyesters, andcomplex esters.

The diesters are prepared from dicarboxylic acids fully esterified withmonohydric alcohols, or from glycols fully esterified withmonocarboxylic acids. The total number of carbon atoms in the diestermolecule is about 20 to 36, preferably 22 to 26. Preferred dicarboxylicdiesters are those of the formula:

ROOCR'COOR wherein each R may be the same or different and representsthe straight or branched chain alkyl radical of an alkanol having about6 to 13 carbon atoms, and R is a straight or branched chain C to Cdivalent saturated aliphatic hydrocarbon radical. Examples of suchdiesters include: di-Z-ethylhexyl sebacate, di-n-nonyl adipate, di-C Oxoazelate, di-n-heptyl isosebacate, di-C 0x0 adipate, di-C Oxo adipate,di-Z-ethylhexyl adipate, di-C, 0x0 adipate, di-C 0x0 trimethyl adipate,di-C Oxo pimelate, etc. Other operable diesters are those prepared fromglycols and monocarboxylic acids such as dipropylene glycoldipelargonate and polyethylene glycol 200 dicaproate. Diesters preparedfrom the 0x0 alcohols, which are isomeric mixtures of branched chainaliphatic primary alcohols, are particularly desirable. The Oxo alcoholshave a very high degree of branching in the hydrocarbon chain, whichresults in diester oils having low pour points and low viscosity at lowtemperature. These alcohols are prepared from olefins, such as polymersand copolymers of C and C monoolefins, which are reacted with carbonmonoxide and hydrogen in the presence of a cobalt-containing catalystsuch as a cobalt carbonyl catalyst, at temperatures of about 300 to 400F., and under pressures of about 1000 to 3000 p.s.i. to form aldehydes.The resulting aldehyde product is then hydrogenated to form the 0x0alcohol which is then recovered from the hydrogenation product.

Operable polyesters are prepared by reacting polyhy- 'dric alcohols suchas trimethylolpropane and pentaerythritol with monocarboxylic acids suchas butyric acid, caproic acid, caprylic acid, pelargonic acid, etc. togive the corresponding trior tetraesters.

The complex esters which may be used as the base oils are formed byesterification reactions between a dicarboxylic acid, a glycol, and analcohol and/or a monocarboxylic acid. These esters may be represented bythe following formulas:

wherein R and R are alkyl radicals of a monohydric alcohol (e.g.alkanols), or a monocarboxylic acid (e.g. alkanoic acids), R and R arehydrocarbon radicals of dicarboxylic acids (e.g. alkandioic acids), andR and R are divalent hydrocarbon or hydrocarbon-oxy radicals, such as CH(CH or or CH CH(CH )OCH CH(CH derived from an alkylene glycol orpolyalkylene glycol. n in the complex ester molecule, will usually rangefrom 1 to 6 and is controlled by the relative molar ratio of the glycolor polyglycol to the dicarboxylic acid. In preparing the complex ester,there will always be some simple ester formed, i.e. n=0, but this willgenerally be a minor portion.

Some specific materials used in preparing the above types of complexesters are as follows: alkanols having 6 to 13 carbon atoms such asn-butyl alcohol, 2-ethylbutyl alcohol, 2-ethylhexanol, n-hexyl alcohol,C Oxo alcohol and C Oxo alcohol, etc.; the corresponding fatty ormonocarboxylic acids; dicarboxylic acids and glycols of the same typedescribed as useful in the preparation of the acidic partial esters ofthe invention. In addition the corresponding thioglycols may be used. Ingeneral these complex esters will have a total of 20 to 80, preferably30 to 50, carbon atoms. These complex esters and methods for theirpreparation are known in the art and have been described in variouspatents.

The lubricating compositions of the invention will comprise a majorproportion of a synthetic ester lubricating oil and about 0.01 to 2.0%,preferably 0.1 to 0.5 wt. percent of the acidic partial ester additive.The composition can also include other additives (e.g. 0.01 to 10.0 wt.percent) such as oxidation inhibitors such as phenothiazine,phenyl-a-naphthylamine, p-amino diphenyl amine; viscosity indeximprovers such as polymethacrylates, polystyrene; anti-foamants such asdimethylsilicone polymers; anti-wear agents; additional loadcarryingagents; corrosion inhibitors; etc.

The invention will be further understood by the following examples:

EXAMPLE I An acidic partial ester was prepared as follows:

Into a 1,000 ml. round-bottom 3-neck flask fitted with a stirrer,thermometer and a reflux condenser with a water trap was placed 808grams (4.0 moles) of sebacic acid and 364 grams (2.0 moles) ofPolyethylene Glycol 200 (PEG 200a commercial polyglycol having anaverage molecular weight of about 182). 60 ml. of heptane as a waterentraining agent was also introduced. No esterification catalyst wasemployed. The mixture was then refluxed at atmospheric pressure and to afinal liquid temperature of 225 C. while stirring for 2 hours. Thecalculated amount of water (4 moles) was collected in the trap. Theresulting residue was stripped of volatiles at 200 C. under a jet ofnitrogen and about 1100 grams of a white semi-solid acidic partial esterwas obtained. This material may be represented by the following wordformula:

Sebacic acid-PEG 200-sebacic acid EXAMPLE II 2 moles of sebacic acid wasreacted with 1 mole of hexanediol-2,5 following the procedure of ExampleI.

EXAMPLE III 4 moles of adipic acid was reacted with 2 moles ofpolyethylene glycol 200 following the procedure of Example I.

EXAMPLE IV 2 moles of adipic acid was reacted with 1 mole ofhexanediol-2,S following the procedure of Example I.

EXAMPLE V 2 moles of adipic acid was reacted with 1 mole of2-ethyl-hexanediol-1,3 following the process of Example I.

The products of Examples I through V, described above, were added to adiester base oil composition and tested for lead corrosion. The diesterbase composition was a 50/50 volume mixture of a di-C Oxo adipate and adi-C Oxo adipate which mixture contained 1 wt. percent of phenothiazineas an oxidation inhibitor. The Oxo portions of the adipates were derivedfrom Oxo alcohols prepared from a C -C olefin feed.

Several of the products of Examples I through V were also added to acomplex ester having the general formula:

C Oxo alcohol-(adipic acid-polyethylene glycol 200) -adipic acid-C Oxoalcohol wherein x averaged about 1.7. This complex ester also contained0.5 wt. percent of phenothiazine as antioxidant and 0.01 wt. percent ofa silicone anti-foamant.

The above compositions were tested in a lead corrosion test which wascarried out by rapidly rotating a bi-metallic strip consisting of a leadstrip and a copper strip bound together in an oil sample maintained at325 F. while air was bubbled through the sample. The weight loss of thelead strip is then determined and reported in terms of milligram weightloss per sq. inch of lead surface. The compositions tested and theresults obtained are summarized in the following table:

Table I LEAD CORROSION TEST 1 Hr. Lead Corrosion (mg. ml) TestComposition 1 Diester 3.8 15.2 141 326 2 Diester +0.275 wt. percentsebacic acid-PEG 200-sebacic acid 0.6 1.2 1.3 3.1 3 Diester +0.5 wt.percent sebacic acid-PEG 200-sebacic acid. 0 0.2 0.2 .2 4 Dlester +0.5wt. percent sebacic 0.2 0.4 0.8 1.0

acid-hexanediol-Z,5-sebacic acid. 5 Diester +0.44 wt. percent adtpic 0 00 0 acid-PEG 200-ndipic acid. 6 Diester +0.2 wt. percent adlpic 0 0 00.2

ncid-hexanediol-2,5-adipic acid. 7 Diester +0.22 wt. percent ad p c 0.20.6 1.1 1.3

acifi-Z-ethyl hexanediol-1,3-ad1p1c aci 8 Complex ester- 5 29 251 9Complex ester +1.5 wt. percent 0 0.2 .6 .8

adipic acid-PEG 200-adipic acid. 10- Complex ester +1.5 wt. percent 0.21.2 2.3 3.5

sebacic acid-PE G 200-sebacic acid.

The above table demonstrates the remarkable effectiveness of thecompositions of the invention in reducing lead corrosion caused by theester base oils. Thus, the diester base composition (Test 1) showedconsiderable corrosivity to lead. However, the addition of varyingamounts of the acidic partial esters of Examples I through V drasticallyreduced the amount of corrosion (see Tests 2 to 7). In fact, Test 5shows that .44 wt. percent of the product of Example III completelyeliminated lead corrosion. Tests 8 to 10 demonstrate the effectivenessof the acidic partial esters with a complex ester base oil composition.

Several of the blends of Table I were further tested for corrosivenessto copper, magnesium, iron, aluminum and silver and for changes inviscosity and acidity. These tests were carried out in accordance withMILL-7808-C specification procedure, i.e., by immersing weighed stripsof the metal to be tested in a 100 cc. of the sample maintained at 347F. for 72 hours while bubbling 0.5 liter per hour of air through thesample. The metal strip is then re-weighed to determine the weightchange as mg./cm. and the change in viscosity and neutralization numberof the composition is determined. The compositions tested and theresults obtained are summarized in Table II which follows:

Table II OXIDATION-CORROSION STABILITY 347 F. Oxidation-CorrosionStability Composition Corrosion, mgJcm Via/100 Neut. F., Change PercentCu Mg Fe Al Ag Change Diestor 0. 01 0. 01 0. 01 0. 0. 01 0. 8 3. 4Diester +0.275% sebacic acid-PEG-ZOO-sebacic 0. 05 0. 05 0. 07 0. 06 0.07 0. 9 1. 4 Dlester +0.15% sebacic acid-PEG-200'sebacie Mid 0. 13 0. 070.09 0. 08 0. 11 0. 9 2. 2 Somplex llilgsttenmnin5 -gu nu di fiabbu 0.340.01 0.05 0.05 -0.01 1.4 10.0

om ex ser se 2010 act seb eic magi"? 0.04 0.06 02 03 0- 00 0.1 15 0 Asshown by Table H, there is no significant change in corrosion of theabove five metals by use of the acidic partial esters of the invention.The change shown is within the tolerance allowed for products of thissort.

Several of the compositions of Table I and Table II were next tested forload-carrying ability in the Ryder Gear Test in accordance withMIL-7808C specification procedures and in a modified SAE load-carryingtest. In the modified SAE test, the Standard SAE lubricant tester wasused except that a gear ratio of 3.4:1 was used in place of theconventional ratio of 14.6:1. The test was carried out by running themachine for two minutes under a 50 lb. load and then manually increasingthe load 50 lbs. every ten seconds until scuffing occurred. Thecompositions tested and the results obtained are summarized in Table IIIwhich follows:

Table III LOAD CARRYING ABILITY As seen by the above table, theadditives of the invention are also useful for imparting load-carryingability to synthetic ester lubricating oils.

While the prior examples have shown the reaction of 2 molar proportionsof a dicarboxylic acid per 1 molar proportion of a glycol, a lessermolar proportion of the dicarboxylic acid may be used. To illustrate,Example I is repeated by reacting 3 moles of the sebacic acid with 2moles of the Polyethylene Glycol 200.

tions of a C to C alkandioic acid with one molar pro portion of a C to Cglycol.

2. A lubricating oil composition according to claim 1, wherein said acidpartial ester is formed by the esterification of two molar proportionsof said alkandioic acid with one molar proportion of said glycol.

3. A lubricating oil composition according to claim 1, wherein saidglycol is a polyalkylene glycol.

4. A lubricating oil composition according to claim 1, wherein saidglycol is an alkylene glycol.

5. A lubricating oil composition according to claim 1, wherein saidglycol contains 4 to 18 carbon atoms.

6. A lubricating oil composition according to claim 1, wherein saidsynthetic ester lubricating oil consists of a hydrocarbon chaininterrupted by ester linkages.

7. A lubricating oil composition according to claim 1, wherein saidester lubricating oil is a diester having the formula ROOCR'COOR whereinR is a C to C alkyl group and R is a C to C saturated hydrocarbonradical.

8. A lubricating oil composition comprising a major amount of acarboxylic acid ester lubricating oil and dissolved therein about 0.01to about 0.5 wt. percent of the esterification reaction produce of about2 moles of a C to C alkandioic acid with 1 mole of a C to C glycol.

9. A lubricating oil composition according to claim 8, wherein saidester lubricating oil is a diester, said alkandioic acid is an adipicacid and said glycol is a polyethylene glycol having an averagemolecular weight of about 182.

References Cited in the file of this patent UNITED STATES PATENTS2,788,326 Bondi et a1 Apr. 9, 1957 2,918,433 Buckmann Dec. 22, 19592,929,786 Young et al Mar. 22, 1960 2,960,469 Young Nov. 15, 1960

1. A LUBRICATING OIL COMPOSITION COMPRISING A MAJOR AMOUNT OF CARBOXYLICACID ESTER LUBRICATING OIL AND WITHIN THE RANGE OF 0.01 TO ABOUT 2.0 WT.PERCENT, BASED ON THE WEIGHT OF SAID ESTER OIL, OF AN ACID PARTIAL ESTERDISSOLVED FICATIONS PRODUCT OF ABOUT 1.7 TO ABOTU 2.0 MOLAR PROPORTIUONSOF A C4 TO C12 ALKANDIOIC ACID WITH ONE MOLAR PROPORPORTION OF A C2 TOC36 GLYCOL.